Vibratory work machines such as, for example, vibratory compactors, are well known. Typically, vibratory work machines such as compactors for soil, gravel, asphalt or the like include vibrator mechanisms that are configured to provide one or more frequency settings as well as one or more amplitude settings. In operation, the vibration amplitude and vibration frequency of a vibratory compactor may be varied by a user to suit a particular application. For example, the vibration amplitude and frequency suitable for compacting gravel for a road may be different from the vibration amplitude and frequency suitable for compacting soil for a footpath.
Typically, vibratory compactors include vibrator mechanisms that produce vibrations using two or more weights that rotate about a common axis. The weights are eccentrically positioned with respect to the common axis and are typically movable with respect to each other about the common axis to produce varying degrees of imbalance during rotation of the weights. As is commonly known, the amplitude of the vibrations produced by such an arrangement of eccentric rotating weights may be varied by positioning the eccentric weights with respect to each other about their common axis to vary the average distribution of mass (i.e., the centroid) with respect to the axis of rotation of the weights. As is generally understood, vibration amplitude in such a system increases as the centroid moves away from the axis of rotation of the weights and decreases toward zero as the centroid moves toward the axis of rotation. It is also well known that varying the rotational speed of the weights about their common axis may change the frequency of the vibrations produced by such an arrangement of rotating eccentric weights.
In one known type of vibratory mechanism, the eccentric weights may be held in position relative to each other during use of the vibrator mechanism, but a fluent mass such as metallic shot, metal members, steel balls, liquid metal, sand or other shiftable ballast material disposed within a chamber to vary the amplitude of the vibrations. One example of this type of vibratory mechanism is provided in U.S. Pat. No. 4,586,847 to Stanton, the disclosure of which is incorporated by reference herein. The chamber is configured so that the fluent mass shifts within the chamber as the eccentric weight rotates in either the clockwise (CW) or counter clockwise (CCW) direction so that the fluent mass is located adjacent an eccentric weight when a shaft rotates in one direction of rotation, and is located diametrically opposite the eccentric weight when the shaft rotates in the opposite direction of rotation. The shifting of the fluent mass disposes the centroid of the eccentric weights at two different positions and, correspondingly, creates two different vibratory amplitudes based on the direction of rotation. In typical implementations, the vibratory motor provides the same frequency for rotation in both the CW and CCW directions (one vibration frequency with two amplitudes), or one frequency in the CW direction and a different frequency in the CCW direction (two vibration frequency/amplitude combinations). Consequently, the vibratory compactor is limited to two vibration characteristics.
Other types of vibration frequency and amplitude control strategies exist in the art. For example, U.S. Pat. No. 7,089,823 to Potts provides a speed control system wherein the vibration frequency is determined based on the amplitude selected by the operator of the vibratory work machine. A controller of the vibratory mechanism includes an amplitude control circuit that generates an amplitude control signal that varies from a minimum value to a maximum value. The vibratory mechanism is adapted to vibrate at an amplitude based on an amplitude control signal characteristic. Additionally, the controller includes a frequency control circuit that is operatively coupled to the amplitude control circuit to produce a frequency control signal that varies based on the amplitude control signal characteristic. Consequently, operator selects the amplitude of the vibrations, and the controller determines the corresponding frequency of the vibrations based on its programming. The operator is not provided with independent control of the frequency such that one vibration frequency for each vibration amplitude that can be set by the operator.
In view of this, a need exists for providing a vibrator mechanism control system in which an operator may select for multiple available discrete combinations of vibration frequencies and amplitudes of a vibrator mechanism.